This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The significance of this study is that the data obtained will determine whether or not increased bone resorption is contributing to the decrease in bone mineral density (BMD) found in children after hematopoietic cell transplantation (HCT) leading to osteopenia and osteoporosis. This study aims to (1) evaluate bone mineral resorption in children following HCT to determine if increased bone mineral resorption contributes to the osteoporosis found in children after HCT, (2) to confirm the decrease in BMD 6 months after HCT, and (3) to correlate changes in the markers of bone resorption with changes in BMD over a period of 6 months following HCT.